local a = {
  __newindex = function(table, key, value)
    rawset(table, key, value + 3)
  end
}

local b = {}
setmetatable(b, a)
b.key1 = 15
b.key1 = 5
b.key2 = 8
print(a.key1)
print(b.key1)
print(b.key2)
